Question

When a liquid in a closed container reaches a state of equilibrium with its vapor, which of the following is true?

A. The number of molecules in the vaper state and liquid state or equal.
B. The number molecules evaporating and condensing are equal.
C. The processes of the evaporation and condensation have ceased.
D. The liquid is at the boiling point.

Answer 1

The true answer is (B) The number molecules evaporating and condensing are equal. If evaporation takes place in an enclosed area, the escaping molecules accumulate as a vapour above the liquid. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapour increases. When the process of escape and return reaches an equilibrium, the vapour is said to be "saturated", and no further change in either vapour pressure and density or liquid temperature will occur.
(https://en.wikipedia.org/wiki/Evaporation#Evaporative_equilibrium )